Grass mowing machines known as zero turning radius (“ZTR”) mowers have at least one independently powered drive wheel on each side of a frame. One drive wheel may be operated in a forward direction while the other drive wheel may be stopped or operated in reverse. Many ZTR mowers have a twin stick control system. A pair of steering arms or control levers may be provided side-by-side, with each steering arm controlling one of the drive wheels. When both steering arms or control levers are advanced together forwardly out of their neutral position, both drive wheels rotate forwardly to cause the mower to move forward. A ZTR mower may be steered by advancing one steering arm or control lever more than the other.
Typically, each steering arm or control lever on a ZTR mower may be linked to a pump arm of one of two separate hydraulic pumps, or of a dual hydraulic pump; i.e., a separate pump for each wheel. The steering arm or control lever may be used to move a pump swash plate through a direct linkage.
The steering arms or control levers on a ZTR mower may be mounted on the vehicle frame so that each has a first pivot axis allowing the steering arm or control lever in the operating position to pivot forwardly in an arc to turn the wheel in forward, or pivot rearwardly to turn the wheel in reverse. Additionally, when a steering arm or control lever is in neutral, between forward and reverse, the operator may pivot it outwardly on a second pivot axis. The ZTR mower may stay in neutral when the steering arms or control levers are pivoted outward.
Some ZTR mowers have mechanisms to engage park brakes when the steering arms or control levers are pivoted outward. For example, U.S. Pat. Nos. 6,434,917 and 6,729,115 for Mower with Combined Steering and Brake Levers relates to linkages connected between each steering lever and brake mechanism, which engages or releases a park brake when the steering lever is moved laterally outward from then neutral position. U.S. Pat. No. 6,739,116 for Powered Actuator System for Mower Parking Brake System relates to an electrically powered actuator system that includes a solenoid that may be de-energized or energized to engage or disengage the parking brake. U.S. Pat. No. 7,677,371 for Mower With Automatic Parking Brake relates to a hydraulic parking brake actuator that senses the position of the steering lever and controls a valve for high pressure fluid to flow to the actuator to disengage the parking brake. U.S. Pat. No. 7,686,108 for Electrically Released parking Brake for Zero Turn Radius Mower relates to switches that allow air cylinders to exhaust pressurized air so that tension springs may actuate the brakes. U.S. Pat. No. 8,240,420 for Steering Mechanism relates to a sensor for activating parking brakes for sensing the lever assembly when it is in the outboard position. U.S. Pat. No. 8,573,368 for Motor Driven Parking Brake Actuator System for Mower relates to an electric motor that drives a gear reduction assembly rotating an output shaft linked to the parking brakes. U.S. Pat. No. 9,313,953 for Parking Brake System for a Lap Bar Controlled Zero Turn Radius Mower relates to an actuation assembly with a rotatable push arm connected to the lower end of each lap bar, and is spaced apart from a rotatable pedal arm in a disengaged position, and in contact in an engaged position.